A clutch conventionally comprises a reaction plate, a movable pressure plate, and a friction disk mounted between said reaction and pressure plates. Movement of the pressure plate is controlled by a diaphragm, which is turn controlled by a release bearing. The friction disk is rotationally linked to an input shaft of a gearbox, and the reaction plate is, for example, rotationally integral with a flywheel linked to the driving shaft, for example a crankshaft of an internal combustion engine.
The release bearing is controlled by an actuator regulated by an electronic calculator so as to exert a predetermined force on the diaphragm and displace it a given distance.
The pressure plate is thus movable between an engaged position in which the friction disk is clamped between said pressure plate and reaction plate, and a disengaged position in which the friction disk is released.
It is known to use a release bearing having a tubular body through which the input shaft of the gearbox is intended to pass, an actuator having a tubular movable part, also called a “piston,” engaged in an annular receptacle of the body and movable in translation parallel to the axis of the body. The piston of the actuator is intended to operate a clutch diaphragm, for example by way of a ball bearing. The piston is thus movable between an engaged position in which a driving torque is transmitted to the input shaft of the gearbox, and a disengaged position in which no torque is transmitted to said shaft.
A bearing of this kind thus comprises an actuator of the concentric slave cylinder (CSC) type.
As is known from the document FR 2 985 555 in the name of the Applicant, and from the document EP 1 898 111, the release bearing can be equipped with a target whose position is representative of the position of the movable part of the actuator, and with a detector capable of detecting the position of the target. In the case of the two aforementioned documents, the detector is arranged radially outside of the target and the body, resulting in a significant radial space requirement.
The documents DE 10 2009 056 380 and US 2012/0146625 disclose release bearings allowing the operation of double clutches.
As is known, a double clutch in particular allows the driving shaft of the vehicle to be coupled alternatively to two coaxial input shafts of a gearbox, which latter can be automated.
A double clutch thus allows the gear ratio to be changed while maintaining the transmission of a driving torque to the wheels of the vehicle. This is because the two clutches are associated respectively with even- and odd-numbered gear ratios. During a gear ratio change, a first clutch is disengaged while the second clutch is engaged, so that driving torque is transferred progressively from the first to the second clutch.
Each clutch comprises a mechanism having a diaphragm intended to interact with a pressure plate that is rotationally integral with the engine's shaft. Each diaphragm is displaceable by means of a corresponding release bearing between an inactive position and an active position. Depending on the type of clutch, the active position of the diaphragm corresponds to a coupling or decoupling of the engine and gearbox shafts, and the inactive position of the diaphragm corresponds to a decoupling or coupling of said shafts. The terms used are thus a “normally open” and a “normally closed” clutch.
For safety reasons, at least one of the clutches is of the normally open type.
The release bearing is controlled by an actuator regulated by an electronic calculator so as to exert a predetermined force on the diaphragm and displace it a given distance.
The pressure plate of each clutch, impinged upon by the corresponding diaphragm, is intended to clamp a friction disk against a corresponding reaction plate. A reaction plate can be provided for each clutch. As a variant, a single reaction plate that is common to both clutches is used, mounted between the two friction disks.
Each friction disk is rotationally linked to an input shaft of the gearbox, and each reaction plate is, for example, rotationally integral with a flywheel linked to the driving shaft. Clamping a friction disk between the corresponding pressure plate and reaction plate thus allows a torque to be transmitted between the driving shaft and the associated gearbox shaft.
In case of a double clutch, the associated release bearing conventionally has two actuators, specifically a first actuator whose piston allows displacement of the diaphragm of the first clutch, and a second actuator whose piston allows displacement of the diaphragm of the second clutch. The two pistons are coaxial and extend into coaxial annular chambers of the body of the release bearing.
In the document DE 10 2009 056 380, each piston is equipped with a target intended to interact with a radially external detector. The target that is part of the radially inner piston passes through an opening of the body as well as the radially external piston, so that said target is located facing toward the aforesaid detector. A structure of this kind requires an increase in the axial dimension, and thus the space requirement, of the release bearing. In addition, given the proximity of the two targets, undesired interference can exist between the targets and/or the associated detectors, which is detrimental to efficiency and to measurement precision.
In the document US 2012/0146625, the target and the detector associated with the first piston operate on a different detection principle from the target and detector associated with the second piston, in order to avoid any interaction between the targets and detectors located close to one another. A first detector can be, for example, of the magnetic type, the other detector then being non-magnetic. This prevents the use of two detectors of the same kind, for example two Hall-effect, PLCD, or inductance detectors, which are inexpensive detectors that are reliable even in environments subjected to vibration and to large temperature swings.